Exhaust processing apparatus

ABSTRACT

An exhaust processing apparatus comprises a cracking furnace for cracking and solidifying exhaust discharged from a reactor for forming crystals on a semiconductor substrate, a first collecting device for collecting relatively large components solidified in the cracking furnace, a second collecting device for collecting relatively small solidified components passed through the first collecting device, and a chemical or a physical adsorbing member for chemically or physically adsorbing the exhaust passed through the first and second collecting devices. 
     The apparatus may be provided with bypass piping for bypassing a particular section of the apparatus, a shutoff member for opening and closing the bypass piping and a control device for controlling the shutoff member. 
     The cracking furnace of the apparatus has a heating portion for heating the exhaust, an enlarged portion disposed downstream the heating portion and having a passage whose cross-sectional area is larger than that of the heating portion, and a cooling mechanism for forcibly cooling the heated exhaust.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust processing apparatus adoptedfor, for instance, a semiconductor vapor deposition apparatus.

2. Description of the Prior Art

In growing semiconductor crystals, there are a liquid phase crystalgrowing technique and a vapor deposition technique. Compared to theliquid phase crystal growing technique, the vapor deposition techniquehas a high controllability to easily grow crystals in multilayerstructure and is able to control the composition ratio of crystalsaccording to the partial pressure ratio of source gases.

Due to these advantages, the vapor deposition technique has beendeveloped rapidly in these days. Particularly, a metalorganic chemicalvapor deposition (MOCVD) apparatus for growing thin film crystals on asemiconductor substrate is excellent to control the speed of crystalgrowth, easy to operate and adequate for mass production so that it iscatching many attentions.

FIG. 1 is a view showing one example of the vapor deposition apparatus.In the figure, a reactor 105 has a gas inlet 101 and a gas outlet 103. Asusceptor 109 is disposed inside the reactor 105 to hold and heat asemiconductor substrate 107. The susceptor 109 is supported with arotary shaft 111 which is rotatably supported with a bottom wall 105a ofthe reactor 105 and rotated by a motor (not shown). The reactor 105 hasa high-frequency induction heater 113 to heat the susceptor 109.

The semiconductor substrate 107 is held on the susceptor 109 and heatedto a predetermined temperature with the susceptor 109 which is heatedwith the high-frequency induction heater 113. After that, source gasesfor growing crystals are introduced from the gas inlet 101 into thereactor 105. The source gases react on the semiconductor substrate 107to grow crystals on the substrate due to the reaction and decompositionof the source gases.

If a GaAs film, for example, is to be formed on the semiconductorsubstrate 107, H₂ is used as a carrier gas and trimethylgallium (TMG)which is organometal and arsine (AsH₃) which is hydride are reacted ingas phases.

After the reaction and decomposition, the source gases which remainunreacted flow through a space 115 between a periphery 109a of thesusceptor 109 and an inner wall 105b of the reactor 105 and isdischarged through the gas outlet 103 to the outside of the reactor 105.

In this vapor deposition apparatus, the unreacted exhaust dischargedfrom the gas outlet 103 includes noxious hydrides such as the arsine andorganometal so that various exhaust processing apparatuses shall beinstalled to treat the noxious exhaust.

FIG. 2 is a view showing an example of the exhaust processingapparatuses. An exhaust processing apparatus 117 comprises a crackingfurnace 119, a filter 121 and a chemical trap (a chemical adsorbingmember) which are successively disposed in an exhaust flowing directionin the middle of piping 118 connected to the gas outlet 103 of thereactor 105.

The cracking furnace 119 has a heater 125 to heat the exhaust includingthe unreacted source gases passing through the cracking furnace 119 tocrack, for instance, part of arsine contained in the exhaust into solidarsenic and hydrogen.

The solid arsenic is collected with the filter 121 disposed downstreamthe cracking furnace 119. Arsine which has not solidified and passedthrough the filter 121 is adsorbed with an adsorbing material 127 in thechemical trap 123. With the combination of the cracking furnace 119 andthe filter 121, an amount of the arsine to be treated with the chemicaltrap 123 may be reduced to improve the service life of the chemical trap123.

However, according to the apparatus mentioned in the above, the finerthe filter 121, the higher the collecting efficiency of solidifiedarsenic as well as the exhaust pressure. As a result, a dischargingperformance is decreased and an operation at a predetermined pressurehindered. Therefore, the apparatus 117 shall be designed stronger, andsealing structures for connections of the piping 118 stricter

In addition, the arsenic solidified in the cracking furnace 119 may clogthe filter 121 and piping 118. This may give adverse effects on growingcrystals on the semiconductor substrate 107, or may temporarily stop thecrystal growth.

Further, in such a conventional apparatus, arsenic vapor generated dueto the decomposition may flow out of the cracking furnace 119 andsolidify outside the cracking furnace 119 to form dusts to increase loadof the dust collecting filter 121. Compared to a cross-section area of apassage of the cracking furnace 119, a diameter of the piping 118 on thedownstream side of the cracking furnace 119 suddenly reduces. As aresult, unreacted source gases contained in heated exhaust are cooledand solidified around a connection of the piping 118 to clog the piping118.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an exhaust processingapparatus which can improve a collecting efficiency of unreacted sourcegases without increasing exhaust pressure.

Another object of the present invention is to provide an exhaustprocessing apparatus having an extended durability which can securelycollect unreacted source gases contained in exhaust while suppressingpressure loss.

Still another object of the present invention is to provide an exhaustprocessing apparatus which can secure an exhaust passage even if thepressure of exhaust passing through a cracking furnace and a collectingdevice exceeds a predetermined value.

Still another object of the present invention is to provide an exhaustprocessing apparatus which can improve an efficiency in removingunreacted source gases contained in exhaust to prevent an exhaustpassage from clogging.

In order to accomplish the objects and advantages mentioned in theabove, the present invention provides, in one aspect, an exhaustprocessing apparatus comprising a cracking furnace disposed on thedischarging side of a reactor. In the reactor, source gases are suppliedto a semiconductor substrate supported inside the reactor to growcrystals on the substrate. Reacted source gases and unreacted sourcegases are discharged from the reactor to the cracking furnace in whichpart of the unreacted source gases is cracked and solidified. Theexhaust processing apparatus further comprises a first collecting devicefor collecting relatively large components among those solidified in thecracking furnace, a second collecting device disposed downstream thefirst collecting device and collecting relatively small components amongthe solidified components passed through the first collecting device,and a chemical or a physical adsorbing member for chemically orphysically adsorbing the exhaust passed through the first and secondcollecting devices.

With this arrangement, unreacted source gases among exhaust dischargedfrom the reactor are partly cracked and solidified in the crackingfurnace. After that, relatively large components among the solidifiedcomponents are collected with the first collecting device whilerelatively small components passed through the first collecting deviceare collected with the second collecting device. The unreacted sourcegases passed through the first and second collecting devices arechemically or physically adsorbed with the chemical or the physicaladsorbing member

According to another aspect of the present invention, there is providedan exhaust processing apparatus which comprises a cracking furnacedisposed on the exhausting side of a reactor In this reactor, sourcegases are supplied to a semiconductor substrate supported inside thereactor to form crystals on the substrate. Reacted source gases andunreacted source gases are discharged from the reactor. The exhaustprocessing apparatus further comprises a collecting device forcollecting components solidified in the cracking furnace, a chemical ora physical adsorbing member for chemically or physically adsorbing theexhaust passed through the collecting device, bypass piping forbypassing a section between the reactor and the chemical or the physicaladsorbing member, a shutoff member for opening and closing the bypasspiping, and a control device for controlling the shutoff member. Thecontrol device opens the shutoff member when the pressure of exhaustpassing through the cracking furnace and collecting device exceeds apredetermined value.

With this arrangement, when the pressure of exhaust passing through thecracking furnace and collecting device exceeds the predetermined value,the control device opens the shutoff member to flow the exhaust from thereactor to the chemical or physical adsorbing member.

According to still another aspect of the present invention, there isprovided an exhaust processing apparatus comprising a cracking furnacedisposed on the exhausting side of a reactor. In the reactor, sourcegases are supplied to a semiconductor substrate supported inside thereactor to grow crystals on the substrate. Reacted and unreacted sourcegases are discharged from the reactor. The exhaust processing apparatusfurther comprises a collecting device for collecting solid componentssolidified in the cracking furnace. The cracking furnace has a heatingportion for heating the exhaust and an enlarged portion disposeddownstream said heating portion and having a passage whosecross-sectional area is larger than that of the heating portion.

With this arrangement, exhaust from the reactor is heated and cracked inthe heating portion of the cracking furnace. After that, the exhaust isexpanded in the enlarged portion to slow a flowing speed of the exhaust,thus increasing the solidification rate of the unreacted source gasesand preventing the solidified components from clogging an outlet of theheating portion.

According to still another aspect of the present invention, there isprovided an exhaust processing apparatus comprising a cracking furnacefor decomposing unreacted gases contained in exhaust discharged from avapor deposition reactor The cracking furnace comprises a heatingportion for heating and decomposing the exhaust, an enlarged portiondisposed downstream the heating portion to collect the decomposedcomponents, a cooling mechanism disposed inside the enlarged portion tocool the decomposed components, and an outlet connected to the enlargedportion to discharge a carrier gas in the enlarged portion.

According to this arrangement, the vapor of reactive products isforcibly cooled and solidified with the cooling mechanism and adheres tothe cooling mechanism so that the decomposed products can be surelycollected in the enlarged portion. The decomposed products will notescape from the outlet, thus preventing the outlet from clogging toreduce replacement frequencies of filters disposed on the downstreamstages.

These and other objects, features and advantages of the presentinvention will become apparent from the following descriptions ofpreferred embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section schematically showing a reactor of a vapordeposition apparatus to which an exhaust processing apparatus isapplied;

FIG. 2 is a schematic view showing a conventional exhaust processingapparatus fitted to the reactor shown in FIG. 1;

FIG. 3 is a schematic view showing an exhaust processing apparatusaccording to a first embodiment of the present invention;

FIG. 4 is a schematic view showing an exhaust processing apparatusaccording to a second embodiment of the present invention;

FIGS. 5 and 6 are schematic views showing modifications of the secondembodiment shown in FIG. 4 respectively;

FIG. 7 is a schematic view showing a cracking furnace used for the firstand second embodiments of the present invention; and

FIGS. 8 to 13 are schematic views showing cracking furnaces according toother embodiments of the present invention respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a view showing an exhaust processing apparatus according tothe first embodiment of the present invention.

Firstly, the constitution of a reactor 1 will be described. The reactor1 has a gas inlet 3 and a gas outlet 5. At a bottom wall la of thereactor 1, there is rotatably supported a rotary shaft 7 which in turnsupports a susceptor 9. The susceptor 9 holds a semiconductor substrate11 and is rotated with a motor (not shown). The reactor 1 has ahigh-frequency induction heater 13 for heating the semiconductorsubstrate 11 to a predetermined temperature.

Piping 15 of the exhaust processing apparatus is connected to the gasoutlet 5 of the reactor 1. In the middle of the piping 15, a crackingfurnace 17, a cyclone 19, a membrane filter (a first collecting device)21, a depth filter (a second collecting device) 23 and a chemical trap(a chemical adsorbing member) 25 are successively disposed in an exhaustflowing direction.

The cracking furnace 17 has a heater for heating exhaust discharged fromthe reactor 1. Therefore, part of unreacted source gases such as arsinecontained in the exhaust is cracked in the cracking furnace 17 intoarsenic (solidified components) and hydrogen to flow toward the cyclone19.

The cyclone 19 has a cylindrical upper portion and a funnel-like lowerportion. The exhaust is introduced into the upper portion of the cyclone19 in a tangential direction and swirls. Due to a centrifugal action ofthe exhaust, part of the arsenic contained in the exhaust hits an innerwall of the cyclone 19 and drops downward while the exhaust flows upwardthrough a center pipe.

The membrane filter 21 has relatively coarse meshes. When the exhaustpasses through the filter 21, relatively large arsenic components arecollected with it because the large arsenic components cannot passthrough the filter 21. Since the meshes of the filter 21 are relativelycoarse, pressure loss of the exhaust is small.

The depth filter 23 has fibrous material such as a nonwoven cloth withrelatively fine meshes. The fibrous material has a certain thicknessalong the direction of the flow of exhaust. When the exhaust passesthrough the filter 23, relatively small solidified arsenic componentspassed through the membrane filter 21 hit the fibrous material and arecompletely collected with the filter 23. Namely, the small solidifiedarsenic components hit the meshes of the fibrous material to tanglearound the fibers and are completely collected with the fibers. Sincethe collecting principles of the filters 21 and 23 are different fromeach other, pressure loss of the exhaust passing through the depthfilter 23 is relatively small.

The chemical trap 25 contains a chemical adsorbing member. The chemicaladsorbing member is, for instance, a material for chemically adsorbingarsine.

An operation of this embodiment will be described.

Unreacted source gases which have not contributed to reaction in thereactor 1 are discharged as exhaust from the gas outlet 5 into thepiping 15. The exhaust is introduced into the cracking furnace 17 inwhich the unreacted source gases such as arsine are cracked into solidarsenic and hydrogen.

The exhaust containing the solidified arsenic flows to the cyclone 19 inwhich part of the arsenic is removed from the exhaust. Then, themembrane filter 21 collects relatively large arsenic, and the depthfilter 23 completely collects the remaining solidified arsenic. Thearsine passed through the filters 21 and 23 is chemically adsorbed inthe chemical trap 25, and the remaining exhaust is discharged outside.

As described in the above, according to the first embodiment of thepresent invention, the membrane filter 21 for collecting relativelylarge arsenic, the depth filter 23 for collecting relatively smallarsenic and the chemical trap 25 for adsorbing arsine are sequentiallydisposed in an exhaust flowing direction. Accordingly, arsenicsolidified in the cracking furnace 17 and arsine not solidified can besurely removed from the exhaust.

The membrane filter 21 which is coarse and causes small pressure losscollects roughly the relatively large solidified arsenic, and the depthfilter 23 which is disposed downstream the membrane filter 21 and causessmall pressure loss surely collects the small solidified arsenic so thatthe total pressure loss may be small. Namely, since the membrance filter21 has relatively coarse meshes, the membrance filter 21 causes a largecollecting capacity and small pressure loss The depth filter 23 causes alarge collecting capacity and a large pressure loss. However, initialpressure loss is sufficiently small, therefore, it is able to collectthe small solidified arsenic. With both the filters 21, 23, there isachieved an exhaust processing apparatus which is capable of collectingthe small solidified arsenic and causing a large collecting capacity andsmall pressure loss. Therefore, the exhaust smoothly flows toward thechemical trap 25 to improve the durabilities of the filters 21 and 23and chemical trap 25.

Since the total pressure loss is small, exhaust pressure is not neededto be set to a high value, an operation pressure maintained at apredetermined value, and the sealing structure of a connection of thepiping 15 need not to set strictly.

The present invention is not limited to the above-mentioned embodimentbut the cyclone 19 may be omitted to realize the same effect only withthe filters 21 and 23 and chemical trap 25.

As the second collecting device, an electric dust collector may be usedinstead of the depth filter 23. In this case, corona discharge isutilized to give electric charge to the solidified arsenic to separatethe charged particles by Coulomb force.

The chemical trap 25 may be replaced with a physical adsorbing member torealize the same effect.

The second embodiment of the present invention will be described withreference to FIGS. 4 to 6.

The second embodiment is provided with a bypass passage which is forbypassing filters and piping when the filters and piping are temporarilyclogged with solidified arsenic, etc.

In the figures, the same elements as those of the first embodiment shownin FIG. 1 are represented with the same reference numerals to omit theirexplanations.

As shown in FIG. 4, bypass piping 29 is arranged between a gas outlet 5of a reactor 1 and a chemical trap 25. The upstream side of the bypasspiping 29 is connected to a branching portion 15a of piping 15 and thedownstream side to a branching portion 15b.

In the middle of the bypass piping 29, a first shutoff valve (a shutoffmember) 31 is disposed to open and close the bypass piping 29. In themiddle of the piping 15 between the branching portion 15a and a crackingfurnace 17, a second shutoff valve 33 is disposed. A pressure gauge 35is disposed at the branching portion 15a to detect a pressure of exhaustin the piping 15.

The first and second shutoff valves 31 and 33 and pressure gauge 35 areconnected to a control device 60 comprising a solenoid. The solenoid 60opens the first shutoff valve 31 and closes the second shutoff valve 33when the pressure of exhaust detected with the pressure gauge 35 exceedsa predetermined value.

An operation of the second embodiment will be described.

Unreacted source gases in the reactor 1 are discharged as exhaust fromthe gas outlet 5 into the piping 15. The unreacted source gases such asarsine contained in the exhaust are cracked in the cracking furnace 17into solid arsenic and hydrogen.

The exhaust containing the solidified arsenic flows to a cyclone 19which removes part of the arsenic from the exhaust. Then, relativelylarge arsenic particles are collected with a membrane filter 21, andremaining solidified arsenic particles are completely collected with adepth filter 23. The arsine passed through the filters 21 and 23 ischemically adsorbed with the chemical trap 25, and the remaining exhaustis discharged outside.

When the membrane filter 21 or the depth filter 23 is clogged, apressure of exhaust in the piping 15 increases. When the pressure isdetected with the pressure gauge 35, the solenoid 60 opens the firstshutoff valve 31 and closes the second shutoff valve 33.

As a result, exhaust from the reactor 1 passes through the gas outlet 5and bypass piping 29 to secure an exhaust flowing passage toward thechemical trap 25 where arsine contained in the exhaust is adsorbed. Ifthe reactor 1 is directly connected to the chemical trap 25, the load onthe chemical trap 25 may be increased, but if the direct connection isdown for a short time, almost all the arsine may be absorbed only withthe chemical trap 25.

Then, filter cartridges in the filters 21 and 23 are replaced with newones while the exhaust is passing through the bypass piping 29.

As described above, according to this embodiment, an exhaust passage issecured even if the membrane filter 21 or the depth filter 23 is cloggedso that crystals can be continuously grown on a semiconductor substrate11 in the reactor 1.

A clogging state of the membrane filter 21 or of the depth filter 23 canbe confirmed by detecting a value on the pressure gauge 35.

The present invention is not limited to the above-mentioned embodimentbut the cyclone 19 may be omitted to realize the same effect only withthe filters 21 and 23 and chemical trap 25.

Namely, without the cyclone 19, almost all the arsenic and arsine may beabsorbed, however, with the cyclone 19, the life-times of the filters21, 23 and chemical trap 25 are improved.

The second shutoff valve 33 may be omitted to realize the same effectbecause the exhaust passes through the bypass piping 29 only by openingthe first shutoff valve 31. The first shutoff valve 31 may be manuallyopened and closed.

The chemical trap 25 may be replaced with a physical adsorbing member toachieve the same effect.

Two modifications of the second embodiment of the present invention willbe described with reference to FIGS. 5 and 6, respectively.

In the modification shown in FIG. 5, a depth filter 23' havingrelatively fine meshes is disposed in the middle of bypass piping 29.With this arrangement, even if a first shutoff valve 31 is opened topass exhaust through the bypass piping 29, solid components decomposedand produced in the reactor can be removed with the filter 23'.

In the modification shown in FIG. 6, bypass piping 37 is disposedbetween a cracking furnace 17 and a chemical trap 25. In the middle ofthe bypass piping 37, as in the middle of piping 39, a cyclone 19, amembrane filter 21 and a depth filter 23 are arranged. A first shutoffvalve (a first shutoff member) 31 is disposed on the bypass piping 37 toopen and close the bypass piping 37, while a second shutoff valve 33 isdisposed on the piping 39 between a branching portion 15a and a cyclone19. At the branching portion 15a, a pressure gauge 35 is disposed todetect a pressure of exhaust in the piping 39.

The first and second shutoff valves 31 and 33 and pressure gauge 35 areconnected to a solenoid 60. The solenoid 60 opens the first shutoffvalve 31 and closes the second shutoff valve 33 when, for instance, thepressure of exhaust detected with the pressure gauge 35 exceeds apredetermined value.

According to the modification shown in FIG. 6, when the pressure ofexhaust in the piping 39 exceeds the predetermined value, the exhaust ispassed through the bypass piping 37 to completely remove arsenic, etc.,with the cyclone 19, membrane filter 21 and depth filter 23 on thebypass piping 37, as in the case of the piping 39. While the exhaust arebeing discharged through the bypass piping 37, filtering portions suchas the cyclone 19, membrane filter 21 and depth filter 23 of the piping39 may be replaced with new ones.

Cracking furnaces to be used for the first and second embodiments willbe described with reference to FIGS. 7 to 13, respectively.

Firstly, the cracking furnace 17 of the first embodiment shown in FIG. 3will be described with reference to FIG. 7.

A cross-sectional area of a passage of the cracking furnace 17 is largerthan that of the piping 15. The cracking furnace 17 comprises a heatingportion 17a having a passage whose cross-sectional area is substantiallyuniform through the upstream side and the downstream side thereof, andan enlarged portion 17b disposed downstream the heating portion 17a andhas a passage whose cross-sectional area is larger than that of theheating portion 17a.

Outside the heating portion 17a, a heater 27 for heating exhaust isdisposed to reach the enlarged portion 17b. On the periphery of theenlarged portion 17b, a cooling pipe 18 is disposed as a cooling devicefor forcibly cooling the exhaust heated in the heating portion 17a.

In the enlarged portion 17b, a baffle plate 28 of, for instance,cylindrical shape is arranged downwardly from the top of the enlargedportion 17b. The exhaust is guided along the baffle plate 28 toward thebottom of the enlarged portion 17b and then upward along an inner wallof the enlarged portion 17b which is cooled with the cooling pipe 18.

An outlet 20 of the cracking furnace 17 to the cyclone 19 is locatedupper than a vertical center of the enlarged portion 17b. The outlet 20is laterally arranged with respect to an exhaust flowing direction(vertical in FIG. 7).

An operation of the cracking furnace 17 will be described.

Unreacted source gases in the reactor 1 are discharged from the gasoutlet 5 to the piping 15. After that, the exhaust is introduced intothe heating portion 17a of the cracking furnace 17 and heated with theheater 27. The heated exhaust is introduced into the enlarged portion17b from the heating portion 17a and forcibly cooled with the coolingpipe 18. Arsenic is substantially in a gas phase at a high temperatureand solidified when cooled.

Since the cross-sectional area of the passage in the enlarged portion17b is larger than that of the heating portion 17a, a speed of theexhaust introduced into the enlarged portion 17b is reduced to increasea residence time of the exhaust in the enlarged portion 17b. As aresult, the exhaust is sufficiently cooled to increase a rate ofsolidification of gaseous arsenic. Therefore, a rate of solidifiedarsenic at the outlet 20 is reduced to prevent the passage fromclogging.

The heater 27 is extended to reach just before the enlarged portion 17bso that the solidification of arsenic is not carried out at the lowerportion of the heating portion 17a but is correctly carried out in theenlarged portion 17b. Therefore, the arsenic does not adhere to an innerwall of the heating portion 17a to prevent the passage from clogging.

Due to centrifugal force caused when a flowing direction of the exhaustis changed in the enlarged portion 17b, the solidified arsenic movestoward the bottom of the enlarged portion 17b and collected at there.

The exhaust is guided with the baffle plate 28 toward the bottom of theenlarged portion 17b and then upward along the inner wall of theenlarged portion 17b cooled with the cooling pipe 18, and dischargedthrough the outlet 20. Therefore, a cooling area of the exhaust isincreased to surely solidify arsenic contained in the exhaust.

The exhaust containing the solidified arsenic flows toward the cyclone19 which removes part of the arsenic from the exhaust. After that,relatively large arsenic particles are collected with the membranefilter 21, and the remaining solidified arsenic is completely collectedwith the depth filter 23. The arsine passed through both the filters 21and 23 is chemically adsorbed with the chemical trap 25, and theremaining exhaust is discharged outside.

As described in the above, according to this embodiment, thesolidification of arsenic existing in arsine in the exhaust is promotedto collect the solidified arsenic so that an amount of arsine to beprocessed with the chemical trap is reduced to extend the service lifeof the chemical trap. Further, the passages of exhaust are preventedfrom clogging.

FIG. 8 is a view showing a cracking furnace according to anotherembodiment. In the figure, the same elements as those of the previousembodiment are represented with the same reference numerals to omittheir explanations.

According to this embodiment, a cooling pipe 18 is disposed inside anenlarged portion 17b. The enlarged portion 17b has no baffle plate 28 ofthe previous embodiment, and the cross-sectional area of a passage inthe enlarged portion 17b is gradually reduced from the upstream side tothe downstream side. In this embodiment the total length of the coolingpipe 18 may be reduced to achieve the same effect as that of theprevious embodiment.

FIG. 9 is a view showing a cracking furnace according to still anotherembodiment. In the figure, a cracking furnace 17 comprises a heatingportion 17a, a metal mesh 30 disposed inside the heating portion 17a,and a heater 27 disposed around the heating portion 17a. The upper part(upstream side) of the heating portion 17a is connected to thedischarging side of a reactor (not shown). The lower part of the heatingportion 17a is connected to an enlarged portion 17b which is to collectdecomposed products. The enlarged portion 17b can be disassembled intoupper and lower segments to remove the collected decomposed products. Acooling mechanism 32 comprises a helical pipe disposed just under theheating portion 17a. Inside the cooling mechanism 32, coolant such aswater is flown from the outside of the enlarged portion 17b. An outlet20 is connected to a side wall of the enlarged portion 17b to dischargegases.

With this arrangement, exhaust (unreacted source gases and the carriergas) from the reactor are introduced from an inlet of the crackingfurnace 17 to the heating portion 17a. The unreacted gases introducedtogether with the carrier gas through the inlet are heated to apredetermined temperature and contact with or pass through the metalmesh 30 to become vapor of reacted products. The vapor of reactedproducts exits from the heating portion 17a and reaches the coolingmechanism 32 where the vapor is forcibly cooled. When the vapor ofreacted products is cooled, solidified decomposed products adhere to thecooling mechanism 32. The decomposed products not adhered to the coolingmechanism 32 accumulate on the bottom of the enlarged portion 17b.Namely, the decomposed products are collected on the cooling mechanism32 having a wide area and on the bottom of the enlarged portion 17b sothat exhaust discharged from the outlet 20 contains almost no decomposedproducts and the vapor of reacted products.

As described in the above, according to the cracking furnace of thisembodiment, the cooling mechanism 32 is disposed inside the enlargedportion 17b to forcibly cool the vapor of reacted products so that thedecomposed products are surely collected in the enlarged portion 17b. Asa result, the decomposed products and the vapor of reacted products arerarely discharged from the outlet 20 to remarkably reduce clogs in theoutlet 20 and frequency of filter replacement.

FIGS. 10 to 12 are sectional views showing cracking furnaces accordingto other embodiments respectively. In the figures, the same parts asthose shown in FIG. 9 are represented with the same reference numeralsto omit their explanations. These embodiments have cooling mechanismswhich are different from the cooling mechanism 32 of the embodiment ofFIG. 9.

A cooling mechanism 32 of the cracking furnace shown in FIG. 10 has adisk member 34 having a passage 36 formed inside the disk member 34 toflow coolant. A plurality of through openings 38 for passing exhaust areformed on the disk member 34 perpendicular to the disk member 34.

A cooling mechanism 32 of the cracking furnace shown in FIG. 11 has anannular cooling pipe 40 provided with fins 42 which are obliquely fittedto the inside of the cooling pipe 40. The fins 42 may be disposed inparallel with the cooling pipe 40, and the cooling pipe 40 may bedisposed in the plural number.

A cooling mechanism 32 of the cracking furnace shown in FIG. 12 has anenlarged portion 17b in which a plurality of fins (plate members) 44 aredisposed to extend a gas passage in the enlarged portion 17b. The fins44 are alternately fitted to an inner wall surface of the enlargedportion 17b and cooled with a cooling pipe 46. Intervals between thefins 44 may be narrowed gradually from the top toward the bottom of theenlarged portion 17b to increase a collecting efficiency. The coolingpipe 46 may be bent such that contact areas with respect to the fins 44are increased.

With this arrangement, the cooling mechanism 32 forcibly cools vapor ofreacted products to solidify decomposed products, which adhere to thecooling mechanism 32 to realize the same effects as those of theprevious embodiments.

FIG. 13 is a sectional view showing a cracking furnace according tostill another embodiment. In the figure, the same parts as those shownin FIG. 9 are represented with the same reference numerals to omit theirdetailed explanations.

A difference of this embodiment from the previous embodiments is that acooling mechanism 32 is vibrated. The cooling mechanism 32 has aplurality of bellows pipes 48 connected in parallel with each other andis disposed just under a heating portion 17a of a cracking furnace 17.The cooling mechanism 32 is supported by a side wall of an enlargedportion 17b of the cracking furnace 17 through a bellows flange 50. Thecooling mechanism 32 is horizontally vibrated from the outside of theenlarged portion 17b.

With this arrangement, when a certain amount of decomposed productsadhere to the cooling mechanism 32, the cooling mechanism 32 is vibratedhorizontally to drop the decomposed products from the cooling mechanism32. Since the decomposed products are not strongly adhering to thecooling mechanism 32, large part of the decomposed products drop fromthe cooling mechanism 32 due to the vibration. If a large amount of thedecomposed products adhere to the cooling mechanism 32, it may clog thelower part of the heating portion 17a of the cracking furnace 17 todeteriorate a cooling efficiency of the cooling mechanism 32. Therefore,by periodically vibrating the cooling mechanism 32, the heating portion17a is prevented from clogging, and the cooling mechanism 32 canefficiently collect the decomposed products.

In summary, according to the exhaust processing apparatus of the presentinvention, relatively large components among solidified componentssolidified in a cracking furnace are collected in a first collectingdevice, and relatively small components are collected in a secondcollecting device which is disposed downstream the first collectingdevice. Accordingly, a durability of the apparatus as a whole isimproved while unreacted source gases contained in exhaust are surelycollected with pressure loss being suppressed.

Further, according to the present invention, an exhaust passage issecured even if a pressure of the exhaust passing through the crackingfurnace and collecting devices exceeds a predetermined value. Therefore,crystals can be continuously grown on a semiconductor substrate in areactor with no interruption.

Further, according to the present invention, the sectional area of apassage in an enlarged portion of the cracking furnace which is locateddownstream a heating portion of the cracking furnace is larger than thatof the heating portion so that the solidification of components isaccelerated in the cracking furnace to improve, with the cooperation ofthe collecting devices disposed on the downstream side, a service lifeof the apparatus as a whole.

Further, according to the present invention, the exhaust is forciblycooled and solidified with a cooling mechanism provided for the crackingfurnace so that the solidified products can be collected in the crackingfurnace.

Various modifications will become possible for those skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

What is claimed is:
 1. An exhaust processing apparatus comprising:acracking furnace disposed on a discharging side of a reactor forcracking and solidifying part of unreacted source gases contained inexhaust emitted from the reactor which supplies source gases to asemiconductor substrate supported inside the reactor to grow crystals onthe substrate and discharges the exhaust containing reacted source gasesand the unreacted source gases; first collecting means having a firstmember with a plurality of holes for collecting relatively largecomponents solidified in said cracking furnace, said first collectingmeans being constructed to pass relatively small components and gasesand to collect the relatively large components by colliding saidrelatively large components with a surface of said first member; andsecond collecting means having a second member with a predeterminedthickness in an exhaust gas outflowing direction and disposed downstreamsaid first collecting means to arrest relatively small solidifiedcomponents passed through said first collecting means, said secondcollecting means being constructed to pass gases and to arrest saidrelatively small components in said second member.
 2. The exhaustprocessing apparatus as claimed in claim 1, further comprising:adsorbingmeans for chemically and/or physically adsorbing an exhaust passedthrough said first and second collecting means.
 3. The exhaustprocessing apparatus as claimed in claim 2, wherein said firstcollecting means comprises a cake-filtration medium having relativelycoarse meshes for collecting the relatively large solidified componentsdischarged from said cracking furnace.
 4. The exhaust processingapparatus as claimed in claim 3, wherein said second collecting meanscomprises a depth filtration medium having means for completelyarresting in it the relatively small solidified components passedthrough the cake-filtration medium.
 5. The exhaust processing apparatusas claimed in claim 4, wherein the solidified components arresting meanscomprises a nonwoven cloth.
 6. The exhaust processing apparatus asclaimed in claim 2, further comprising:bypass piping for connectingbetween the reactor and said adsorbing means.
 7. The exhaust processingapparatus as claimed in claim 6, further comprising:shutoff means foropening and closing said bypass piping; and control means forcontrolling said shutoff means such that said shutoff means is openedwhen the pressure of the exhaust passing through said cracking furnaceand first and second collecting means exceeds a predetermined value. 8.The exhaust processing apparatus as claimed in claim 5, wherein saidbypass piping includes a second depth filter which collects solidparticles finer than those collected with said membrane filter.
 9. Theexhaust processing apparatus as claimed in claim 2, furthercomprising:bypass piping for connecting between said cracking furnaceand said adsorbing means.
 10. The exhaust processing apparatus asclaimed in claim 9, wherein said bypass piping includes:a secondmembrane filter having relatively coarse meshes for collectingrelatively large components solidified in said cracking furnace; and asecond depth filter for substantially completely collecting relativelysmall solidified components passed through the second membrane filter.11. The exhaust processing apparatus as claimed in claim 8, furthercomprising:shutoff means for opening and closing said bypass piping; andcontrol means for controlling said shutoff means such that said shutoffmeans is opened when the pressure of the exhaust passing through saidfirst and second collecting means exceeds a predetermined value.
 12. Theexhaust processing apparatus as claimed in claim 2, wherein saidadsorbing means comprises either a chemical adsorbing member forchemically adsorbing at least the source gases or a physical adsorbingmember for physically adsorbing at least the source gases.
 13. Theexhaust processing apparatus as claimed in claim 1, wherein saidcracking furnace comprises a heating portion provided with a heatingmeans for heating the exhaust, and an enlarged portion disposeddownstream said heating portion and having a passage whosecross-sectional area is larger than that of said heating portion. 14.The exhaust processing apparatus as claimed in claim 13, wherein saidenlarged portion is provided with a cooling means for forcibly coolingthe exhaust heated in the heating portion.
 15. The exhaust processingapparatus as claimed in claim 14, wherein said cooling means is disposedalong the periphery of the enlarged portion.
 16. The exhaust processingapparatus as claimed in claim 15, wherein the enlarged portion isprovided with a baffle plate for guiding the exhaust along an inner wallof the enlarged portion and for changing a flowing direction of theexhaust.
 17. The exhaust processing apparatus as claimed in claim 14,wherein said cooling means is disposed inside the enlarged portion. 18.The exhaust processing apparatus as claimed in claim 17, wherein thecooling means comprises a pipe disposed just under the heating portionto flow coolant through the pipe.
 19. The exhaust processing apparatusas claimed in claim 17, wherein the cooling means comprises a pipedisposed just under the heating portion to flow coolant through thepipe, and fins connected to the surface of the pipe.
 20. The exhaustprocessing apparatus as claimed in claim 17, wherein said cooling meanscomprises a plurality of plate members disposed inside the enlargedportion to extend a passage formed inside the enlarged portion, and acooling pipe for cooling the plate members.
 21. The exhaust processingapparatus as claimed in claim 17, wherein the cooling means comprises apipe for flowing coolant, the pipe being able to .be vibrated in theenlarged portion.
 22. An exhaust processing apparatus comprising:acracking furnace disposed on a discharging side of a reactor forcracking and solidifying part of unreacted source gases contained inexhaust emitted from the reactor which supplies source gases to asemiconductor substrate supported inside the reactor to grow crystals onthe substrate and discharges the exhaust containing reacted source gasesand the unreacted source gases; collecting means for collectingcomponents solidified in said cracking furnace; adsorbing means forchemically and/or physically adsorbing an exhaust passes through saidcollecting means; a piping for connecting the reactor, said crackingfurnace, said collecting means, and said absorbing means; and a bypasspiping for directly connecting the reactor to said adsorbing means. 23.The exhaust processing apparatus as claimed in claim 22, furthercomprising:shutoff means for opening and closing said bypass piping; andcontrol means for controlling said shutoff means such that said shutoffmeans is opened when the pressure of the exhaust passing through saidcracking furnace and collecting means exceeds a predetermined value. 24.An exhaust processing apparatus comprising:a cracking furnace disposedon a discharging side of a reactor for cracking and solidifying part ofunreacted source gases contained in exhaust emitted from the reactorwhich supplies source gases to a semiconductor substrate supportedinside the reactor to grow crystals on the substrate and discharges theexhaust containing reacted source gases and the unreacted source gases;first collecting means for collecting components solidified in saidcracking furnace; adsorbing means for chemically and/or physicallyadsorbing an exhaust passed through said first collecting means; apiping for connecting the reactor, said cracking furnace, said firstcollecting means, and said adsorbing means; and bypass piping fordirectly connecting the cracking furnace to said adsorbing means. 25.The exhaust processing apparatus as claimed in claim 24, wherein saidbypass piping includes second collecting means for collecting componentssolidified in said cracking furnace.
 26. The exhaust processingapparatus as claimed in claim 25, further comprising:shutoff means foropening and closing said bypass piping; and control means forcontrolling said shutoff means such that said shutoff means is openedwhen the pressure of the exhaust passing through said first collectingmeans exceeds a predetermined value.
 27. In an exhaust processingapparatus for cracking, solidifying and collecting part of unreactedsource gases contained in exhaust discharged from a reactor in whichsource gases are supplied to a semiconductor substrate supported insidethe reactor to grow crystals on the substrate and discharged as theexhaust containing reacted and unreacted source gases, a crackingfurnace for cracking and solidifying part of the unreacted source gases,comprising:a heating portion provided with heating means for heating theexhaust discharged from the reactor; and an enlarged portion disposeddownstream said heating portion and having a passage whosecross-sectional area is larger than that of said heating portion. 28.The cracking furnace as claimed in claim 27, wherein said enlargedportion is provided with a cooling means for forcibly cooling theexhaust heated in said heating portion.
 29. The cracking furnace asclaimed in claim 28, wherein the cooling means is disposed along theperiphery of said enlarged portion.
 30. The cracking furnace as claimedin claim 29, wherein said enlarged portion is provided with a baffleplate for guiding the exhaust along an inner wall of said enlargedportion and for changing the flowing direction of the exhaust.
 31. Thecracking furnace as claimed in claim 28, wherein the cooling means isdisposed inside said enlarged portion.
 32. The cracking furnace asclaimed in claim 31, wherein the cooling means comprises a pipe disposedjust under said heating portion to flow coolant through said pipe. 33.The cracking furnace as claimed in claim 31, wherein the cooling meanscomprises a pipe disposed just under said heating portion to flowcoolant through said pipe, and fins connected to the surface of saidpipe.
 34. The cracking furnace as claimed in claim 31, wherein thecooling means comprises a plurality of plate members disposed insidesaid enlarged portion to extend a passage within said enlarged portion,and a cooling pipe for cooling said plate members.
 35. The crackingfurnace as claimed in claim 31, wherein the cooling means comprises apipe for flowing coolant, said pipe being able to be vibrated in saidenlarged portion.
 36. An exhaust processing apparatus comprising:acracking furnace disposed on a discharging side of a reactor forcracking and solidifying part of unreacted source gases contained inexhaust emitted from the reactor which supplies source gases to asemiconductor substrate supported inside the reactor to grow crystals onthe substrate and discharges the exhaust containing reacted source gasesand the unreacted source gases; a cake-filtration medium for collectingrelatively large components solidified in said cracking furnace; and adepth filtration medium disposed downstream the cake-filtration mediumto collect relatively small solidified components passed through thecake-filtration medium.